The fungus Cryptococcus neoformans causes life-threatening infections in approximately 10% of all patients with AIDS. A considerable body of evidence indicates that antibody to the cryptococcal capsular polysaccharide can contribute to host defenses. We have identified monoclonal antibodies to the capsular polysaccharide antigens. The experimental approach will involve: the study of the molecular structure of individual anticryptococcal antibodies are glycosylated in their antigen binding regions; and the study of serum antibody populations conjugate immunization using rabbit anti-idiotypic reagents and isoelectric focusing. These studies will produce information of fundamental interest in immunology and in the antibody response to fungal antigens. The studies in mice will pave the way for the molecular characterization of the human antibody response. These studies will also produce important information for the development of antibodies of C. neoformans for human therapy and vaccines against this fungal pathogen.